Summary

The histiocytoma is an unsightly but benign skin tumor that tends to arise on the skin of young dogs. While young dogs (under three years of age) are more likely to get these (especially on the face and extremities), they can happen to dogs of any age in just about any location.

Technically, a histiocytoma is an abnormal proliferation of histiocytes in the skin. Histiocytes are cells that function as part of the immunological barrier against invaders that would attempt an “attack” on the skin. In the case of histiocytomas, the self-regulatory reproductive mechanism of these histiocytes is clearly in disarray.

Though they’re considered ugly by most owners’ standards, these masses are benign. In fact, if left untreated they’ll spontaneously resolve within two to three months or less.

Many closely related but far less benign conditions are referred to as histiocytic disorders. In dogs, these include malignant histiocytosis, cutaneous histiocytosis, systemic histiocytosis, histiocytic sarcoma and histiocytic lymphoma.

Though they share the same family, these histiocytic disorders are far more aggressive conditions. As a general rule, dogs who suffer histiocytomas are not considered predisposed to these diseases.

Symptoms and Identification

Histiocytomas typically appear as small, solitary, hairless lumps, usually on the head, neck, ears, and limbs. In some uncommon cases (in the case of Shar peis, in particular), multiple masses may be present at the same time.

These masses are usually less than 2.5 cm in diameter and may or may not be red and ulcerated on their surface.

Cytology can be very helpful for initial diagnosis, but isn’t typically considered definitive. Observation of regression or full histopathology upon removal are usually required by way of achieving definitive diagnosis.

Affected Breeds

Any dog can be affected by these masses but some breeds are predisposed. Labrador Retrievers and Boxers, for example, make the short list. These tumors can also affect Shar Peis, Bulldogs, American Pit Bull Terriers, American Staffordshire Terriers, Scottish Terriers, Greyhounds, and Boston Terriers, among others.

Treatment

Histiocytomas are considered highly treatable skin masses. Though they will typically regress spontaneously within a couple of months, they don’t always do so quickly or completely enough for a veterinarian’s (or owner’s) comfort. In other cases, their appearance (gross or cytological) may begin to defy the standards for this tumor type.

Any deviation from the expectation that the mass in question will prove benign is sufficient inducement to remove it as soon as possible. This determination depends on the veterinarian’s assessment of the mass’s location, size, appearance, cytological appearance, and degree of local inflammation, among other possible factors, including the patient’s history (of past skin masses, for example).

Veterinary Cost

The cost of histiocytomas depends, to a large extent, on whether they’re surgically treated or not. This expense is typically relegated to the price of initial cytology (sometimes omitted), pre-anesthetic labwork, anesthesia, surgical excision (complete removal), and biopsy. A typical outlay usually ranges from $300 to $1,000, depending on the level of care elected (generalist vs. specialist) and the geographic locale.

Prevention

There is no known means of prevention for histiocytomas. However, limiting the breeding dogs with a known hereditary predisposition to histiocytomas is doubtless of some assistance here.

References

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Moore P, Schrenzel M, Affolter V, Olivry T, Naydan D (1996). "Canine cutaneous histiocytoma is an epidermotropic Langerhans cell histiocytosis that expresses CD1 and specific beta 2-integrin molecules". Am. J. Pathol. 148 (5): 1699–708. PMC 1861573. PMID 8623937.

Morrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed.). Williams and Wilkins. ISBN 0-683-06105-4.

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"Tumors with Histiocytic Differentiation". The Merck Veterinary Manual. 2006.

 

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